1. Field of the Invention
The present invention relates to a method of reducing feedbacks on a temporary flow of current drawn from a network, during an operation of an inductive load, with a rectifying circuit, wherein the method including active filtering of harmonics of a network fundamental component with a booster converter.
The present invention also relates to a booster converter implementing the method according to the present invention.
2. Description of the Prior Art
With many electronic apparatuses, in particular, power supply units, control gear, drive control units of all types and the like, the network a.c. voltage is rectified and is smoothed, e.g., with a capacitor. When a load is applied to the rectified d.c. voltage, the d.c. voltage becomes more or less ripple, and the temporary flow of the current drawn from the network substantially deviates from a sinusoidal shape and has a relatively high harmonic component. The so-called network feedbacks obviously depend on a type of the load and its current consumption. Mandatory standards prescribe threshold values or threshold curves for an allowable harmonic component dependent on the operating current.
For reducing or for eliminating such network feedbacks, filter circuits are used which are connected between a network rectifier and the load. A known active filter circuit is shown in FIG. 6. A so-called booster converter and a power factor control circuit (not shown in FIG. 6) make it possible to draw from a network, within allowable power limits and independent of possible variations of the load, current of an approximately sinusoidal shape. The booster converter includes connected, between the output of a network rectifier (6) with a smoothing capacitor (4) and a further smoothing capacitor (5), a choke (1) (a high set-up choke), a diode (3), and a shunt arm of a capacitor (5). Between the choke (1) and the anode of the diode (3), there is provided another shunt arm in a form of an electronic switch (2) actuated by the power factor control circuit. In addition, as shown in FIG. 6, a passive prefilter (7) is arranged in front of the network rectifier (6). The above described active-passive feedback filtering circuit shown in FIG. 6 is described in an article of M. Herfurth, "Active Harmonic Filtering for Line Rectifiers of Higher Output Power," Siemens Components 1/86, p.p. 9-13.
The known network feedback filter presents a problem when the available space is limited and when an apparatus, in particular, a hand-held tool is required to have the smallest possible weight. This is because the choke requires a relatively large and heavy core layout, in particular for drawing a greater power from the network. In the circuit shown in FIG. 6, the choke (1) conducts a d.c. network current. Therefore, the choke should be designed magnetically for a highest current magnitude, i.e., for a maximal amplitude plus a superimposed ripple.
Accordingly an object of the present invention is to provide a method and a power feed circuit which reliably prevent undesirable feedbacks, which act, via the rectifier, on a temporary flow drawn from a network current during operation of an inductive load, wherein the method and the power feed circuit include a filter arrangement having definite advantages with regard to technical expenditures and weight in comparison with conventional network feedback filtering circuits.